Vehicle engines commonly utilize cooling assemblies to remove excess heat from the engine and maintain an optimal operating temperature. The cooling assembly pumps a coolant through the engine and other components in order to control engine temperature. Heat generated within the engine and other components is absorbed by the coolant and dispersed into the surrounding atmosphere through the use of a radiator. In order to improve dispersal by the radiator, it is common to utilize fan assemblies to draw or force air past the radiator to assist in temperature transmission.
It is not always desirable for such fan assemblies to run continuously. At times, it is desirable for the temperature within the coolant to increase rather than decrease. Additionally, continuous operation when unnecessary places a non-required draw on the engine and thereby reduces efficiency. To compensate for this, present fan assemblies utilize fan clutch assemblies that allow for the selective engagement of the fan to the engine such that the fans are engaged only when necessary.
The present invention relates to friction coupling devices that drive radiator-cooling fans. A common friction-coupling device is that of the dry friction drive style, otherwise referred to interchangeably hereinafter with a friction clutch assembly. Dry friction drives are used for their simplicity, cool operating temperature, and ability to turn at fully engaged peak operating speeds.
Although the present invention may be used advantageously in various configurations and applications, it is especially advantageous in a coupling device of the type used to drive a radiator cooling fan of an internal combustion engine for an over the road truck, such as a class 8 truck, and will be described in connection therewith.
Dry friction drives tend to have two operating conditions “ON and OFF”, which refer to when an associated friction clutch is either fully engaged or fully disengaged. When a friction clutch assembly is fully engaged, the assembly provides cooling to an associated engine and is not slipping. When a friction clutch assembly is fully disengaged slippage between the clutch plate and an engagement surface is at a maximum, thus providing little rotational output to drive an associated fan.
There are several disadvantages of known dry friction drives. One disadvantage is damage done to O-rings or seals within the friction clutch assembly. It has been determined that one source of damage done to the O-rings is due to contamination introduced into the environment. Another disadvantage is failure of the bearings within the friction clutch assembly. Bearing failure has been linked with excessive vibrations to the assembly.
These problems stem from the interaction between components in known friction clutch assemblies. There is a spring assembly that resides between the rotating drive shaft and the clutch housing. The spring assembly includes a spring and two end caps, each positioned at one end of the spring. The first end cap is translatable along the piston rod in response to a fluidic control circuit demanding disengagement of the clutch assembly. The first end cap is made from steel and the piston rod is made from steel. Therefore, the steel end cap moves back and forth over the steel piston rod. Internal metal-to-metal contact between the piston rod and spring end cap, sets up the perfect environment for fretting corrosion when coupled with engine vibrations, thus producing significant amounts of oxide particles which contaminate and degrade a nearby seal.
Another problematic issue with known dry friction drives is the costly step of machining radii in the inner diameter of the steel spring end cap.